1. Field of the Invention
This invention is generally concerned with an apparatus and a method for measuring temperature in gas filled enclosures or conduits. More specifically, it is concerned with an improvement for a system involving a pyrometer which is used to measure elevated temperatures in reaction chambers. An example of such chambers is in generators used for the production of synthesis gas via the gasification of hydrocarbon fuels in a partial oxidation process.
A gasification process may include the gasification of gaseous, liquid or solid hydrocarbons containing varying concentrations of ungasifiable ash material. The gasification reactions are carried out at high temperatures and pressures within a reactor vessel which is lined internally with successive courses of refractory material. Depending upon the composition of the hydrocarbon feedstock, the hot gases produced in such a process normally contain entrained particles of unconverted carbon, reacting hydrocarbon fuel, molten ash, and/or non-molten high melting temperature ash material. The interior refractory wall of the reaction chamber used in such a process tends to develop a layer of molten ash which runs doWn the Vertical wall towards a bottom exit.
In a gasification process such as described above, a reliable measurement of reaction chamber temperature is very important. The reliability of the temperature measurement affects many aspects of the gasification operation including control of the reactions, safe process operation, control of the rate of deterioration of the refractory lining and control of the viscosity of the molten ash in order to ensure adequate ash removal through the bottom of the reactor.
With respect to temperature measurement, radiation pyrometers have been used to measure the temperatures of hot surfaces and hot atmospheres such as the interior of gasification reactors or the like. Radiation pyrometric techniques involve measuring the thermal radiation emitted by the hot environment and inferring the temperature from a knowledge of the radiation laws and a knowledge of, or justifiable assumptions about, the emitting characteristics of the surfaces and/or gases being measured.
2. Description of the Prior Art
The solid state radiation detectors used to measure the radiation are fairly delicate and need to be isolated from the hostile atmospheres whose temperatures are being measured. The isolation normally takes the form of a sight glass window and a gas purged sight hole formed through the vessel shell and lining. This provides the detector with a clear optical line-of-sight into the vessel interior.
One weakness of the above method of isolation is that the purged sight hole is subject to becoming blocked whenever the atmosphere being measured contains molten particles. Under such conditions the molten particles will be frozen by the cooler purge gas in the neighborhood of the purged sight hole; and the optical sight path will gradually become occluded by the accumulating material.
One prior art patent addressed to the problem of maintaining an open line-of-sight between a pyrometer and a high temperature reactor is U.S. Pat. No. 4,411,533. The invention comprises a projecting shelf formed integral with the wall and top of the sight hole for diverting molten material away from the top of the hole, and a sloped recess formed integral with the bottom of the sight hole for draining molten material away from the bottom of the hole.
Several difficulties may arise with the above system in practice. When the produced reaction gases carry a high concentration of molten particles, the large volume of molten material running down the interior vertical wall of the vessel overwhelms the capacity of the projecting shelf to divert the material away from the sight hole. In addition, if the molten material is chemically aggressive towards the refractory material used to fabricate the projecting shelf, the shelf will be attacked and will wear away.
However, the chief difficulty arises because the purge gas, which protects the optical window and sight hole from the high temperature gases inside the reaction chamber, tends to also cool the projecting shelf. As a result, the shelf becomes a cold spot which promotes the freezing of any molten material coming in contact with it. Eventually enough frozen material accumulates so that the entire sight hole becomes occluded.
In another prior patent, U.S. Pat. No. 4,400,097, the authors disclose a radiation measuring apparatus including a pyrometer. The latter receives radiation from a gasifier or reactor by way of an elongated measuring duct which is recessed in the refractory lining of the vessel. The measuring duct provides a safety chamber for the prevention of gas leaks from the vessel. The safety chamber is a hermetic housing having two optical windows which are protected from dust and condensation by a purge flow of nitrogen in an inner optical tube. Steam flowing in a second, outer optical tube is used to maintain a clear opening into the reactor. In addition, a third, heat resistant window is used to prevent steam from backflowing into the inner optical tube and condensing on the windows comprising the safety chamber.
The above features permit safe monitoring of the temperature inside a pressurized reaction chamber. However, the apparatus is incapable of readily disposing of, or displacing, material which might accumulate on the inner wall of the reaction chamber near the sight hole opening. Both the nitrogen and the steam will tend to freeze molten material around the hole, thus occluding the sight path. In addition, the third heat resistant window is, nevertheless, a relatively fragile element located in a potentially very destructive region of the vessel. If it were to break during operation, the optical sight path could become distorted and there would be no way to safely replace the window without shutting the process down and removing the entire measuring duct.
Another weakness common to both of the above prior patents is that the final portion of the sight hole nearest the reaction chamber consists simply of the hole drilled through the refractory lining of the vessel. Such holes can easily become distorted or damaged by the intense thermal and mechanical stresses which can prevail inside the contemplated reaction chambers. As a result of differences in thermal expansion coefficients, one layer of refractory may shift with respect to another, thus partially or completely blocking the sight path. Rapidly changing temperatures inside the reaction chamber can give rise to spalling of the refractory around the edges of the hole. When pieces of refractory fall off and the hole enlarges, the sight path is much more difficult to purge and keep clear of obstructions.
In summary, the apparatus provided in the prior art are subject to having their optical sight paths blocked either by accumulation of frozen material around the sight hole opening or by distortion of, or damage to, the portion of the refractory hole nearest the reaction chamber.